This invention relates generally to integrated circuits and more particularly to analog integrated circuits.
As is known in the art, semiconductor integrated circuits generally fall into one of two categories: digital integrated circuits and analog integrated circuits. Digital integrated circuits process signals having one of two discrete signal levels (typically referred to as a logic 1 signal or a logic 0 signal) and include logic gates to process such signals. By contrast, analog integrated circuits either process as input signals thereto and/or produce as output signals therefrom signals having levels which vary in a continuous manner, and include such analog circuits as operational amplifiers, comparators, analog-to-digital converters and voltage regulators, for example. Typically each one of these analog circuits includes a gain stage, that is, a circuit which functions as an amplifier with a gain equal to, greater than, or less than unity, but, in any event, an active circuit.
As is also well-known in the art, one type of digital integrated circuit is commonly referred to as the configurable gate array. Here the integrated circuit manufacturer produces a chip having a large number of identical logic gates arranged in an array. Once such integrated circuit is fabricated, the gates in the array are interconnected by the manufacturer by a final metallization layer selectively in accordance with the overall logic function required by the end user. In this way, the integrated circuit manufacturer is able to produce a large number of identical configurable gate arrays which are suitable for a wide variety of uses, and in response to the particular needs of its customer is able to, in the final metallization process, personalize the integrated circuit to provide logic functions required by its customer. More particularly, the user provides the manufacturer with a logic or truth table relating the logical combinations of logic input signals to produce the desired logic output signals. The relationship between the logic input signals and logic output signals provides the basic functional requirement of the gate array and such is implemented through the final metallization process whereby the individual gates are properly interconnected.
With regard to analog integrated circuits, however, manufacturers typically produce a variety of analog integrated circuit components, each with its own features. The user therefore is required to find the particular component for its needs. Further, the manufacturer generally is required to have an inventory of each of the various components. Recently, there has been a trend to manufacture integrated circuits which include arrays of resistors and three or four types of transistors scattered across the chip. Generally, this approach has been to provide arrays of the various circuit elements in the chip and then interconnect them via the metallization layer selectively in accordance with the circuit desired by the user. Thus, unlike the digital integrated circuit where the gate circuits are each preformed and the personalization is in the interconnection of the gates, here the personalization is in the configuration of the gain stage of the analog circuit itself.